About water and why it is so important:
Since the body continually loses water—2.5 to 3 litres per day—through normal body functions, this water needs to be replaced to keep the body healthy. Ironically, the sensation of thirst occurs only after the body has started to become dehydrated. For this reason it is very important to drink water often, without waiting to feel thirsty. By the time you begin to feel thirsty, the body is already dehydrated to a level of 0.8% to 2% of body weight.